Field of the Invention
The present invention relates to a stage apparatus, a lithography apparatus, and a device manufacturing method.
Description of the Related Art
A semiconductor exposure apparatus is required to have high productivity and finer design rules. Accordingly, a stage to be driven with a substrate or an original placed on it is also required to be driven at a high speed and high accuracy. The stage of an exposure apparatus includes a coarse moving stage to be driven in a long stroke, and a fine moving stage capable of driving along six axes while holding a substrate or an original and arranged on the coarse moving stage. The fine moving stage required to be more accurately driven needs an actuator capable of driving the stage at a high efficiency and high accuracy with little heat. An example of an actuator having such a feature is an electromagnetic actuator using the principle of an electromagnet, which is used as the actuator of a fine moving stage.
The electromagnetic actuator is located to make an electromagnet and a magnetic material to face each other with a small gap. The electromagnet is located on one of the coarse moving stage and the fine moving stage, and the magnetic material is located on the other. An attraction force generated by a magnetic force becomes the thrust of the electromagnetic actuator. When driving the stages at a high acceleration, the fine moving stage is driven following the coarse moving stage by the thrust generated by the electromagnetic actuator.
The thrust generated by the electromagnetic actuator is known to be proportional to the square of a generated magnetic flux. In related arts described in Japanese Patent Laid-Open Nos. 2007-27331 and 2003-168721, a magnetic flux generated in an electromagnet is detected by a coil, and feedback control is performed to make the thrust generated by the electromagnet reach a target thrust.
The thrust generated by the electromagnetic actuator depends on the opposing area between the electromagnet and the magnetic material. In the control methods described in Japanese Patent Laid-Open Nos. 2007-27331 and 2003-168721, to correctly calculate the thrust of the electromagnetic actuator from the magnetic flux detected by the coil, the opposing area between the electromagnet and the magnetic material needs to have a predetermined value. If the thrust of the electromagnetic actuator cannot correctly be calculated, the controller of the actuator cannot correctly control the thrust. For this reason, the target thrust cannot be supplied to the fine moving stage, and the driving accuracy lowers.
When the electromagnet and the magnetic material face along the x or y direction, the opposing area between the electromagnet and the magnetic material changes upon driving the fine moving stage on which the electromagnet or the magnetic material is located in the z direction. Hence, when the fine moving stage is driven in the z direction, the thrust of the electromagnetic actuator cannot correctly be controlled. It is therefore impossible to drive the fine moving stage in the x and y directions at a high acceleration and high accuracy. The fine moving stage is driven in the z direction when aligning an exposure amount measurement sensor or a reference mark on the fine moving stage with the best focus plane of a lens or transferring a substrate from a transportation apparatus to the stage. In this case, a measure of, for example, lowering the driving accelerations in the x and y directions is necessary to prevent the driving accuracy of the fine moving stage from lowering. This impedes an increase in the throughput of the exposure apparatus.